Coking in a fluidized state



March 17, 1959 E. R. CLOUSE ETAL 2,878,162

COKING IN A FLUIDIZED STATE Original Filed May '9, 1950 IN VENTORS.

EASTEN R. CLOUSE RUDOLPH C. WOERNER ATTORNEYS in a coking vessel.

U i a @t ner, Homewood, Ill., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Original application May 9, 1950, Serial No. 160,934, new Patent No. 2,624,697, dated January 6, 1953. Divided and this application January 5, 1953, Serial No. 341,719

1 Claim. (Cl. 202-28) Our invention relates to improvements in the coking of hydrocarbon oils in systems where the coking charge stock is contacted at a coking temperature with a body of adsorbent coke particles maintained in a fluidized state Such a system has been described in Kenneth M. Watson's application Serial No. 121,575 of October 15, 1949, now U. S. Patent No. 2,707,702. According to the Watson invention, the body of coke particles is maintained in the fluidized state and reactor coking is avoided by selectively withdrawing large coke particles as they are built up by adsorption and reaction by means of elutriation. The operation requires a large volume of vaporous fluidizing medium, usually steam, in addition to the vaporous elutriating medium in order to keep the body of coke particles in a fluidized condition. In the operation, appreciable amounts of coke fines are produced by attrition, and under the fluidizing velocities obtaining within the coking vessel tend to be entrained in the reaction vaporous stream withdrawn overhead. The carryover of coke fines is undesirable because they tend to plug the vapor lines and condenser tubes and tend to adversely aflfect the color of the distillate liquid products produced in the process.

According to our invention, fines carryover is suppressed by imposing a whirling motion upon the stream of reaction vapors rising from the body of coke particles maintained in the coking vessel prior to their withdrawal overhead as the vapor product stream. In an especially advantageous aspect of our invention, a substantial portion of the whirling vapor stream is recirculated to beneath the body of coke particles to assist in fluidization. By our invention, process improvement is accomplished by reducing the danger of plugging condenser tubes and in improving the quality of the liquid products. The maintenance of the equilibrium of the system is assisted by return of the coke fines to the main body of coke particles to act as seed nuclei in the coking reaction. The body of coke particles is kept in a well-energized state essential for maintenance of the reaction without wall coking or solidification of the bed while effecting substantial reduction in the quantity of fluidizing medium requred. Our invention will be further described with reference to the accompanying drawing wherein the figure shows in schematic form a reactor which may be employed in the application of our invention.

In the system of the figure, a double wall cooking vessel is employed. The body of adsorbent coke particles is contained within internal cylindrical column 40 disposed within coking vessel 41. The body of coke particles is supported by perforated conical grid 42 and the internal cylindrical column 40 is open at the top. The coking charge stock is introduced to a lower portion of the body of coke particles by means of line 43 and discharge means 44. Coke make is selectively withdrawn from the bottom of the bed through elutriator 45 against the pressure of elutriating steam introduced through connection 46. Steam and reaction vapors separating from p Patented Mar. 17, 1959 the body of coke particles rise out'of internal cylindrical column 40 into the upper section of the'coking' vessel 41 from which they arewithdrawn through overhead vapor line 47 to -'a conventional liquid products'recovery system. Carryover of coke fines from reactor internal cylindrical column, 40 is suppressed by a whirlingmotion imposed upon the rising vapors by rotating impeller 48 connected by shaft 49 to a conventional electric motor or other power device 50. The rotation of impeller 48 not only assists in eliminating coke fines carryover but elfects a. recirculation of steam and reaction vapors down through the annulus 51 formed between internal cylindrical column 40 and the external wall of coking vessel 41 and back into the body of coke particles through conical grid 42. In this way, the quantity of fluidizing medium in line 14 required to keep the bed in a well energized state is significantly reduced.

Because of the reduction in the net requirements for fluidizing medium, a larger diameter bed can be economically employed. Without an economical and eificient means for recirculating fluidizing vapors, undesirably tall towers of small diameter are ordinarily necessary to keep the requirements of fluidizing medium within reasonable limits. The relatively shallow beds of small L/D permitted by operation according to our invention are advantageous with respect to better top-to-bottom mixing so that improved uniformity of contacting is obtained and particle size segregation is avoided.

The form of the impeller employed according to our invention may be varied considerably. A simple propeller type form may be employed having the blades pitched so as to eifect a centrifugal and downward force during rotation. Advantageously, a solid disc with Francis type impeller blades on its lower side may be employed. The speed of rotation depends largely upon the velocity of the rising vapors and the mass of the entrained particles. Relatively low R. P. M.s may be employed, e. g. about 50 to 800 R. P. M.

In operation, the coking vessel is charged with a body of adsorbent coke particles, ordinarily obtained from a previous run, approximating, for example, 10- to SO-mesh in size range. Fluidizing steam at a rate sufficient to maintain a vapor velocity in the vessel of about 2 to 3 feet per second is employed. A coking temperature within the range of about 800 to 1200 F., advantageously 875 to 1050 F., is maintained in the coking reaction vessel. The heat is provided by preheating the feed by heat exchange and by conventional fired heaters. Additional heat is suppled by superheatng the elutriating and fiuidzing media. The pressure in the coking vessel is usually kept low, e. g. usually about atmospheric pressure and within the range of about 10 to p. s. i. Elutriating steam is introduced at a rate suificient to withdraw the net coke make in the form of the larger coke particles.

This application is a division of Serial No. 160,934, filed May 9, 1950, now U. S. Patent No. 2,624,697, granted January 6, 1953.

We claim:

In the coking of hydrocarbon oils by contacting a coking charge stock at a coking temperature with a body of coke particles maintained in a fluidized bed state in a coking vessel from which large coke particles are selectively withdrawn by elutriation and from which reaction vapors are withdrawn overhead, the improvement which comprises coking said hydrocarbon oil in an internal coking zone surrounded by an annular reaction vapor recirculation zone confined within said coking vessel, suppressing entrainment of coke fines in the overhead vapors by imposing a whirling motion upon the stream of sftc'amandaeaction vapors irising from tho-"body 'of'c'bke particles in the .cokinguzoneprior to withdrawal over.-

References Cited in theme-of this patent UNITED STATES PATENTS 2,054,441 Publes Sept. 15; 1936 Publes May 11, 1937 Thomas et a1.- Jan. 29, 1946 Arveson Dec. 17, 1946 Schutte Dec. 21, 1948 heifer Jan. 25, 1949 Kassel Dec. 26, 1950 Clousect a1. Jan. 6, 1953 

